1 Skeletal Muscle Physiology Objectives 1. Structure & function of skeletal muscle 2. Training for power • Anaerobic • Aerobic 3. Strength training Gross Structure Long multi-nucleated fibers Levels of organization: 1. Endomysium: wraps each fiber 2. Perimysium: surrounds several fibers (up to 150) and forms bundles called a fasciculus 3. Epimysium: surrounds all the bundles to form the entire muscle Tendons: • Connective tissue (periosteium of bone to muscle) Origin – more stable bone; Insertion – moving bone Gross Structure (cont.) Sarcolemma: • Muscle cell membrane Satellite cells: • myogenic stem cells located within the sarcolemma Help regenerative cell growth Play a role in hypertrophy Sarcoplasmic Reticulum: • Extensive lattice-like network of tubules and vesicles Provides structural integrity Stores, releases, and reabsorbs Ca 2+ Figure 18.1
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Skeletal Muscle Lecturesuserhome.brooklyn.cuny.edu/jsiegler/Skeletal Muscle Lectures.pdf1 Skeletal Muscle Physiology Objectives 1. Structure & function of skeletal muscle 2. Training
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Skeletal Muscle Physiology
Objectives1. Structure & function of skeletal muscle
2. Training for power• Anaerobic• Aerobic
3. Strength training
Gross StructureLong multi-nucleated fibers
Levels of organization:1. Endomysium: wraps each fiber 2. Perimysium: surrounds several fibers (up to 150)
and forms bundles called a fasciculus3. Epimysium: surrounds all the bundles to form the
entire muscle
Tendons:• Connective tissue (periosteium of bone to muscle)
Origin – more stable bone; Insertion – moving bone
Gross Structure (cont.)
Sarcolemma:• Muscle cell membrane
Satellite cells:• myogenic stem cells located within the sarcolemma
Help regenerative cell growthPlay a role in hypertrophy
Sarcoplasmic Reticulum:• Extensive lattice-like network of tubules and vesicles
Provides structural integrityStores, releases, and reabsorbs Ca2+
Standardize testing protocol• Body position, size & composition• Joint angles• Reps (pre-determined minimum number of trials)• Scoring criteria (select tests with high reproducibility) Figure 22.3
Gender DifferencesSeveral applied approaches to determine whether or not a gender difference exists:
Based on evaluation of:1. Muscle’s cross-sectional area2. Absolute basis of total force exerted3. Architectural characteristics4. Relative to body mass or FFM
Figure 22.4
Greater CSA = greater strength
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Equal strength per CSA Absolute muscle strength greater in men
*muscle mass distribution
Figure 22.6
Little difference in strength when expressed in relative terms
Training for Strength ImprovementMuscles need to be trained close to its current force-generating capacity• Overload Principle
Systematic approach to the Overload Principle:• Progressive resistance training• Isokinetic training• Isometric training
Types of Muscle ContractionsProgressive resistance, isokinetic & isometric training relies on 3 different muscle actions:1. Concentric action
Muscle shortening
2. Eccentric actionMuscle lengthening
3. Isometric actionNo net change in muscle length
Types of Muscle Contractions
ConcentricEccentric
Isometric
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Resistance Training for Children?
Progressive Resistance TrainingProgressive resistance exercise general recommendations (ACSM Guidelines):1. Between 3-RM to 12-RM to improve strength2. Additional 1-RM lifts once per week may
significantly increase strength3. One set is effective if 10-RM is used
Produce most of the health benefitsIncrease compliance2 – 3 days/week is most effective
4. Faster rate of movement improves strength over a slower rate (generally)
Increase weight after 2 weeks• Use 6 – 8 RM• Progress gradually
Work larger muscle groups first & progress to smaller muscle groups
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Other Principles of Strength TrainingCombination of strength & endurance training• Inhibition of strength improvements
Isometric strength training• Limited in ROM & practical application• Beneficial for isolating weakness angles during
rehabilitation
Static vs. dynamic methods• Specificity of the training response (sport performance)• Combination of neural & fiber recruitment
Other Principles of Strength Training (cont.)
Isokinetic resistance training• Provides muscle overload at a preset constant speed
while the muscle mobilizes its force-generating capacity throughout the full ROM
• Theoretically stimulates the largest number of motor units
Isokinetic exercise allows for determination of force-velocity patterns associated with various movements• Also allows for fiber type comparison for a given
movement
Other Principles of Strength Training (cont.)
Plyometric training• Incorporates various
explosive jumping activities to mobilize the inherent stretch-recoil characteristics of the muscle
• Avoid the disadvantage of having to decelerate in the latter part of the joint ROM
Figure 22.15
5 Component Model
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Structural & Functional Adaptations Factors Modifying the Expression of Strength
Psychologic-Neural adaptations:• More efficient neural recruitment patterns• Increased CNS activation• Improved motor unit coordination• Lowered neural inhibitory reflexes• Inhibition of GTO (Golgi Tendon Organs)
Psychologic-neural factors account for most initial strength gains
Figure 22.21 Figure 22.22
Factors Modifying the Expression of Strength (cont.)
Muscular adaptations:• Muscle fiber size (hypertrophy) & strength• Decreased twitch contraction time• Enzymes CK, PFK & myokinase (MK)• Resting levels of ATP, glycogen & PCr • Strength of tendons & ligaments• Bone mineral content
Muscular adaptations include ↓ in:• Body fat & associated changes in BMR• Mitochondria volume & density
Hyperplasia (↑cells) vs. Hypertrophy
General adaptation involves cellular proliferation (increased fiber # or hypertrophy)
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Changes in Fiber-Type Composition
Only changes in recruitment patterns
Training Adaptations & GenderAmount of absolute muscle hypertrophy represents primary difference• Probably resulting from gender-specific differences
in hormonal levelsHigher testosterone levels
Substantial hypertrophy (relative) regardless of gender after/during training
Muscle Strength & Bone Density
Figure 22.29
Circuit Resistance TrainingBenefit of increasing caloric output• Vary according to circuit
Aerobic improvement:• ~ 50% less than improvement observed in cycling or
runningDue to predominance of CRT including upper body exercise
Hypertrophic response:• Lower than traditional resistance training